Help my sick bantam

Hello, I have a sick bantam. She is about a year old and won’t eat or drink and has some clear mucus collecting in her beak. She has been isolated for about a week and I have been giving her water with a syringe that has probiotics and electrolytes in it and I have been putting VetRx poultry aid on her head and under her wings ( seems to be vapor rub for chickens) but nothing is helping. I’m afraid to put her back with my other bantams because I don’t want them to get sick like her. I have no clue what to get or what to do to help my poor bantam. Please anyone help me!